JKL issues Area Forecast Discussion (AFD) at Jul 29, 1:22 PM EDT927
FXUS63 KJKL 291722
AFDJKL
AREA FORECAST DISCUSSION
National Weather Service Jackson KY
122 PM EDT Mon Jul 29 2024
.KEY MESSAGES...
- There is a threat for excessive rainfall from multiple rounds of
showers and thunderstorms through most of the week, which may
lead to localized flooding at times.
- Temperatures climb and humidity builds for Wednesday and
Thursday afternoons when heat indices could reach between 100
and 105 degrees for many locations.
&&
.UPDATE...
Issued at 122 PM EDT MON JUL 29 2024
We have seen an uptick in shower activity this afternoon, with
some activity being heavy at times. This will be the story through
the afternoon and early evening. Very minor updates needed to
include the latest obs and trends.
UPDATE Issued at 1054 AM EDT MON JUL 29 2024
We are see a mid-level wave track across parts of the Ohio Valley
this morning. This has been sparking off showers and a few
thunderstorms at times this morning. Updated the grids to reflect
the latest obs and trends, but outside this only a minor update
overall.
UPDATE Issued at 826 AM EDT MON JUL 29 2024
Have raised the POP this morning for areas where the most
concentrated showers are moving through. However, lowered the
probability of thunder until some heating can occur today, with
very little lightning being detected so far.
&&
.SHORT TERM...(Today through Tuesday)
Issued at 529 AM EDT MON JUL 29 2024
The main concern through the short term period will be timing and
placement of deep convection. We currently have a mid/upper level
trough arriving from the west southwest. Beneath this trough, weak
warm air advection is occurring in the lower levels, resulting in
isentropic lift in the laminar nocturnal flow. Models have been
advertising a redevelopment of convection overnight due to this,
and it got underway after about 07Z. Will look for this to persist
into the morning. As heating and mixing occurs during the day, it
may become surface based for a while, and a peak POP of 60
percent was used. Models indicate slight warming aloft at about
700-800 mb this afternoon. Considering that the surface air mass
will also be getting worked over before this happens, we should
see a decrease in activity late in the day and into this evening.
Another round of convection is forecast for tonight. A modest low
level jet out of the west or west southwest is expected to
develop to our northwest and then drop southeast into KY
overnight. The initial mid/upper level trough will be departed to
our east, but a short wave trough in the west northwest flow aloft
(likely an MCV) on the back side of the departed larger scale
trough should track toward us. The combination of mid/upper level
support and warm air advection/isentropic lift from the low level
jet is expected to result in an MCS dropping southeast over the
area. Confidence in mesoscale features is often lacking well ahead
of time, but all models are suggesting a system, and likely to
categorical POPs have been used for the late night hours into
early Tuesday morning. With high atmospheric moisture indicated
(PWs around 2") there is a concern for excessive rainfall,
especially on the southwest side of the MCS where training cells
would be the most likely. Of course, this would depend on where an
MCS tracks, which is more uncertain.
Heading into the day Tuesday, precip may be ongoing, especially
near the TN and VA borders, but it should be on the decline. This
will leave our atmosphere worked over to start the day. However,
significant destabilization is indicated again by late in the day
(NAM mixed layer CAPE topping 4K J/Kg in our southwest counties).
In the wake of the previous MCS, models are indicating substantial
dry air aloft, which would inhibit sustained convective columns
in the absence of upper level support. With all that said, there
is considerable uncertainty regarding the POP on Tuesday
afternoon, and chance category has been used for the time being.
.LONG TERM...(Tuesday night through Sunday)
Issued at 359 AM EDT MON JUL 29 2024
The models are in good agreement regarding the general long wave
pattern through the rest of the week, although timing of the
smaller scale features does become more problematic by the latter
half of the period. Troughing over the Eastern Seaboard will
gradually diminish and carry on further east through mid-week, as
building 500 mb heights nose in from the Tennessee Valley,
bringing some pseudo-short wave ridging over the Ohio Valley.
This will also result in another surge of heat and humidity.
Meanwhile, additional short wave energy will be inbound from the
northern Plains. This will likely deepen over the Upper Midwest
and into the Great Lakes region by Thursday night, before moving
through the Ohio Valley Friday into Saturday, with an accompanying
surface cold front. Again, timing is questionable, with the GFS
in typical fashion depicting a more progressive outcome, while
the ECMWF is slower. There will also be some inevitable mesoscale
influence. This will keep the threat of locally heavy rainfall
going across eastern Kentucky, with precipitable water values
remaining in the 1.75-2.0" inch range, with bouts of increased
integrated water vapor transport traversing the Ohio and Tennessee
valleys.
Chance PoPs (40-50%) will start out across the area Tuesday
night, with some threat of renewed convection overnight, depending
on how the mesoscale plays out. Chances peak in the 50-60% range
Wednesday, before diminishing a bit through Thursday, as the
rising 500 mb heights engage to our southwest. Temperatures will
top out at around 90 degrees for most locations Wednesday, and
then lower 90s on Thursday. These temperatures, combined with dew
points in the mid 70s, will elevate heat indices to the 100 to 105
degree range during the afternoon hours. PoPs will then return to
the 50-60% range once again Friday through Saturday, as the next
short wave trough and surface cold front gradually approach the
area. Highs will retreat a few degrees. A more decisive lowering
of the PoPs will occur by Sunday, as 500 mb heights rise once
again, shunting the better troughing and associated cyclonic flow
towards the Great Lakes and New England. Lows each night through
early this weekend will likely stay near or just above the 70
degree mark, with the best chance of more widespread 60s arriving
by Sunday morning.
&&
.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 118 PM EDT MON JUL 29 2024
We are seeing a mix of VFR to MVFR skies this afternoon, with
showers popping up across the area this afternoon. This mix if VFR
to MVFR will remain the story for some through the afternoon and
possibly the evening. There remain some uncertainty on a line of
showers and thunderstorms arriving late tonight into Tuesday
morning, but if this system comes through it would lead to IFR or
lower conditions at times tonight into Tuesday morning. This
complex of storms could also lead to some strong to severe wind
gusts at times if this does develop. Overall winds will remain
light and variable through the period.
&&
.JKL WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...DJ
SHORT TERM...HAL
LONG TERM...GEOGERIAN
AVIATION...DJ
Source:
JKL issues Area Forecast Discussion (AFD) at Jul 29, 1:22 PM EDT---------------
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